Perhaps what you're putting in there is not to their liking. I used one with my previous dog and it was her absolute favorite treat. We used peanut butter and...her favorite...cheddar cheese (just cut it up and jammed it in!)
I bought a teething Kong for Topher and he loves it too. I give it to him every night while I'm on the computer and it occupies him for about an hour. He likes cheddar cheese in his. I tried him on the bigger one (the red one) but he still likes the teething one for some reason. Perhaps because it's a bit softer than the red one.
I'd find a treat that they really, really like and jam it in and see if it works.
__________________  VAL, TOPHER AND SOPHIE |